Openings in Exterior Walls: A Cautious Example
Written by: Jonathan Clark
In my May 2022 article I wrote about the code sections which describe the limitations for openings in exterior walls. We explored how the code defines the area of those walls that is used to determine the opening area limitations. The simple take away from that article is the more fire separation distance an exterior wall has, the more allowable opening area there will be within that wall.
About a month after I wrote that article, one of the projects in my office received the following plan check comment, “All V-A Construction Buildings Floor Plans: The porch the segment between two posts shall be considered as exterior walls (see figure for example of locations). Please enclose segment with 1 hour rated wall per CBC Table 601.” (See graphic below for an example of the area referenced)
This was not the first time that we have received a plan check comment like this. Various jurisdictions throughout the Bay Area have made this comment on similar projects as well as third-party plan checkers hired by many jurisdictions. A very detailed reading of this comment seems to mix up a few code sections and leave out others in order to justify that the code doesn’t allow the porch to be open in this situation. I will explain further, but first some background.
To give further context of the graphic above, this is a snapshot of a site plan that shows two separate four-story townhome style buildings that face each other with a paseo between them. This particular snapshot is of two adjacent units in each building that are paired together. The green wall that is labeled “Exterior Wall” is the exterior wall of these units that faces the paseo. The yellow area represents the covered entry porch. Exactly between these buildings we have located the line used to determine the fire separation distance (in my opinion, sometimes incorrectly referred to as the imaginary property line).The other areas colored in green would represent walls that would not be required to be fire-rated due to fire separation and the small red areas represent those walls that would be required to be fire-rated due to fire separation distance. Fire rating based on fire separation distance is found in Table 602.
So how does this plan check comment relate to allowable openings?First, the comment is asserting that the porch columns that support the porch covering are “exterior walls” of the building. Because they are “exterior walls”, they are subject to the allowable opening requirements of Table 705.8. The “opening” in the “exterior wall” is the space between both supporting columns and that cannot exceed 25% (unprotected, sprinklered / walls from 5 to less than 10 feet) or 10% (unprotected, non-sprinklered / walls from 5 to less than 10 feet). The comment doesn’t actually reference or acknowledge that openings are allowed with limitations and requires full enclosure of the porch. (Further the comment gives the reader the impression that the type of construction is what drives the design change, which is also not correct)
This is one of the most challenging plan check comments that we have received that related to allowable openings on many of the projects that we work on. It is challenging because I believe the enforcement agency has to make determinations about what constitutes an exterior wall and an opening that is not supported by the code.
The code defines an exterior wall as follows, “A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane.” This is where I have a hard time finding that the exterior porch columns fall into the definition of an exterior wall. They definitely don’t enclose the building although it is apparent that they provide spatial separation from the surrounding exterior space. Here the enforcing agency has to go outside the definition and then somehow justify how they got there if they are intellectually honest when confronted with an opposing view. We have often theorized that the code definition of an exterior wall should include the concept of it separating exterior from interior space as a way to remove porch areas from being considered exterior walls.
The code doesn’t have an explicit definition for what is considered an opening. It is understood that if the code doesn’t define a term that the common understanding of that term is the intended definition. That being said, I thought maybe an architectural dictionary would define what an opening is in architectural terms, but I couldn’t find one. The closest definition that I could find that has some relevance to architecture was, “an aperture or gap, especially one allowing access.” So I think most of us would agree that an opening is a door, a window, and something that isn’t quite a door or window that allows access. In this case the area between two porch columns could be an opening. But is it an opening in an exterior wall? I would say no.
This is just one example of how the requirements for openings in exterior walls can cause problems for the design of buildings. As noted previously our built environment is continually getting more dense, not less. Many of our current projects are replacing old commercial or industrial land uses with the requirement to reach a certain density of project viability. In addition the State continues to pass legislation that allows more density that local jurisdictions are hard pressed to limit in order to find some relief to the California housing crisis.
Architect | Principal
Comments from Kerwin Lee, AIA: The basic consideration here is for exposure, the effects of a hazard (fire) from one building to another. The building officials’ basic interpretation is correct. This is based on the definition of building and habitable area. The area of a building is defined to include area under any roofed area. This would include porches and other covered areas. There are exceptions for “Projections”. Even when there is a lack of a physical exterior wall, the building (area) needs to be protected as required by the code. This particular question comes up often related to porches, covered areas, including open sides of walks/balconies.
The bottom line answer is how important is it to protect one building from another in this instance and what kind of protection is required to comply with the letter and intent of the code?